1. Field
Example embodiments relate to a thin film transistor (TFT), and more particularly, to a TFT capable of stabilizing an off current.
2. Description of the Related Art
Thin film transistors (TFTs) are used in various application fields and, particularly, are used as switching and driving devices of display apparatuses and as selection switches of cross-point type memory devices.
While liquid crystal display (LCD) apparatuses are mainly used as display panels in televisions (TVs), a large amount of research on organic light-emitting display (OLED) apparatuses that may also be applied to TVs is being conducted. TV display technologies are being developed according to demands of the market. Such demands include demand for large-scaled TVs or digital information display (DID) apparatuses with decreased costs and high definition (high resolution, improved color rendition, improved brightness, improved contrast characteristics, and high color reproducibility). In order to satisfy these demands, substrates, e.g., glass substrates, are required to be larger and TFTs to be used as switching and driving devices of display apparatuses are required for improved performance.
An example of a TFT used as a switching or driving device of a display apparatus is an amorphous silicon (a-Si) TFT which is uniformly formed on a larger substrate of over 2 m in length at a lower cost. However, TFTs are required to have improved performance as display apparatuses, require high-definition characteristics and larger sizes, and thus, the display apparatuses are regarded as being limited by the operating capabilities of typical a-Si TFTs having a mobility of about 0.5 cm2/Vs. Thus, a high-performance TFT having a higher mobility than an a-Si TFT, and a technology of manufacturing the high-performance TFT are required.
A polysilicon (poly-Si) TFT with higher performance than an a-Si TFT has a higher mobility of several tens to several hundred cm2/Vs, and thus, may have a sufficiently high performance to be applied to high-definition display apparatuses, which are not easily implemented by using a-Si TFTs. Also, poly-Si TFTs have less device characteristic deterioration than a-Si TFTs. However, the poly-Si TFT has a relatively high off current while being driven, and therefore, the poly-Si TFT cannot easily function as a switching device of a display apparatus.
In a conventional TFT, the source and drain directly contact a channel. Thus, a strong lateral field may be formed particularly on the drain, an off current of the conventional TFT may be undesirably high, and the conventional TFT may not be stably driven.